> Enceladus is far smaller than the Jovian ocean worlds, roughly the size of Ohio
Why not just say 'has a diameter of about 500 km'? The propensity of astronomers to compare diameters of a small spherical object to a surface patch of a much larger spherical object is intriguing. Similar things happen with 'the Great Red Spot is about two Earths wide'.
t-writescode 13 minutes ago [-]
When trying to describe sizes and scale, having a reference that one of their readers would be able to go "oh, ... that size, huh?" is useful. There's a meme about "Americans will use anything but the metric system" when describing buildings as "100 school buses back to back" or "3 football fields"; but it's to make numbers real and relatable.
If the article said "500km", someone in the comments would go "that's about as wide as Germany!" or similar.
And, since it was km -> "state size", it was almost certainly for the American audience, since they would have used something like the size of Germany for a European, or "twice the size of South Korea" or something.
delta_p_delta_x 6 minutes ago [-]
For science education, I am strongly for using the units directly to describe everything at first, with these looser comparisons in brackets, rather than inline prose. So I would've instead said, 'is 500 km in diameter (roughly the size of Ohio, or Germany from East to West)'. For extremely large or small values I would use scientific notation only, and expect my audience to understand it, because I'd expect their education to be up to mark.
You said these comparisons are made to make things real or relatable; I personally would expect more out of my audience and give them the magnitude and units directly. I'm not writing for a tabloid; having a strong grounding in units understanding without needing to relate to daily phenomena is in my view critical to not making apparently trivial mistakes that can potentially lead to horrible disasters.
merek 1 days ago [-]
Set your calendars:
Europa Clipper, launched 2024, starts Europa flybys on March 2031
Dragonfly, hopefully launching July 2028, arriving on Titan 2034
I am realy excited for the Findings on these missions. Altough I am still missing an Enceladus mission because enceladus is among the most fascinating ocean worlds.
yellowapple 1 days ago [-]
> This remarkable transformation in our understanding is the result of just three missions: Voyager, Galileo, and Cassini—along with some computer modeling and hard staring by the Hubble and Webb space telescopes.
Seems odd to neglect to mention New Horizons immediately after mentioning the probable existence of liquid oceans under Pluto's surface, a finding made possible thanks primarily to New Horizons.
idlewords 9 hours ago [-]
No shade on New Horizons intended, but I was talking about the early 2000's revolution in understanding of ice moons/ocean worlds, and that preceded the Pluto flyby by a lot.
It was a valuable piece of corroborating evidence, but not shocking and unexpected in the way results from those three missions were. We had good reason to believe Pluto would look a lot like Triton, and it does.
yellowapple 8 hours ago [-]
Fair enough, though how common was that belief that Pluto would look like Triton? Before the first photos from New Horizons pretty much every artistic rendition of Pluto I'd seen was a solid ball of rock and/or ice, more like Ceres than Triton.
idlewords 7 hours ago [-]
Both were known to be Kuiper Belt objects, so it was expected there would at least be a family resemblance. I don't think anyone expected Pluto to be more active than Triton; that was certainly a surprise.
If there are planetologists reading the thread, I'd love to hear a more authorative perspective than mine!
exhilaration 1 days ago [-]
Great read, other than Europa I wasn't aware of these other candidate ocean moons.
voxelghost 2 hours ago [-]
All these worlds are yours, except for Europa, attempt no landings there.
miohtama 2 days ago [-]
TIL
> The radiation environment around Europa is punishing; an astronaut standing on the surface would get a fatal dose in about a day
kaseijin 1 days ago [-]
True for all the Galilean Moons more or less. Their orbits all lie within the Jovian equivalent of the Van Allen belts. And Jupiter's magnetic field is much stronger than earth's.
sennalen 1 days ago [-]
Not Callisto. Being within Jupiter's magnetosphere but out of reach of Io's shenanigans makes it one of the mildest radiation environments in the solar system.
stackghost 5 hours ago [-]
I'm interested in learning more about "Io's shenanigans". What are you referring to?
delta_p_delta_x 3 hours ago [-]
Io is in orbital resonance with Europa and Ganymede, which causes its orbit to be slightly elliptical. Due to Jupiter's immense gravitational field strength, Io experiences a very high changing tidal force, which causes a changing stress and strain on the entire structure of Io, which causes tidal heating due to friction. This makes it by far the most volcanically active body in the Solar System. Its surface is regularly completely resurfaced, and is covered in sulfur compounds.
Jupiter and Io have a very interesting symbiosis. Jupiter melts Io to form dusty volcanos. It then magnetically sweeps Io clean of dust. The dust forms a plasma ring that enhances the same magnetic field.
idlewords 1 days ago [-]
Not true at all, the daily dose on Ganymede (which has a magnetic field of its own) is ~70 mSv/day, and Callisto is 0.1 mSv/day.
Io, meanwhile, is 35 Sv/day. Location really matters among the four Galilean moons.
3eb7988a1663 6 hours ago [-]
I was born in a water moon.
pvaldes 2 days ago [-]
Beautifully designed article. Very cool images and diagrams.
> We want rocks in contact with water,
But there is ice compressed between the water column and the xenoceanic bottom, ok. I see the problem.
What about rocks in the surface of the water?. Some volcanic rocks can float.
andrewflnr 13 hours ago [-]
> What about rocks in the surface of the water?. Some volcanic rocks can float.
This is... not something you lay plans on. Even on Earth, these rocks are formed at surface pressure, just barely float, and don't float for long (I've tried). If they form in the deep ocean, I'm guessing the pressure isn't going to let the bubbles be big enough to create bouyancy at all. Either way they would be super rare.
Gravityloss 14 hours ago [-]
I guess I'm now officially old and cranky, as planetoids receiving glow-ups was just a bit much as a term.
9 hours ago [-]
Ozzie-D 8 hours ago [-]
[flagged]
Rendered at 09:14:25 GMT+0000 (Coordinated Universal Time) with Vercel.
> Enceladus is far smaller than the Jovian ocean worlds, roughly the size of Ohio
Why not just say 'has a diameter of about 500 km'? The propensity of astronomers to compare diameters of a small spherical object to a surface patch of a much larger spherical object is intriguing. Similar things happen with 'the Great Red Spot is about two Earths wide'.
If the article said "500km", someone in the comments would go "that's about as wide as Germany!" or similar.
And, since it was km -> "state size", it was almost certainly for the American audience, since they would have used something like the size of Germany for a European, or "twice the size of South Korea" or something.
You said these comparisons are made to make things real or relatable; I personally would expect more out of my audience and give them the magnitude and units directly. I'm not writing for a tabloid; having a strong grounding in units understanding without needing to relate to daily phenomena is in my view critical to not making apparently trivial mistakes that can potentially lead to horrible disasters.
Europa Clipper, launched 2024, starts Europa flybys on March 2031
Dragonfly, hopefully launching July 2028, arriving on Titan 2034
https://en.wikipedia.org/wiki/Europa_Clipper
https://en.wikipedia.org/wiki/Dragonfly_(Titan_space_probe)
Seems odd to neglect to mention New Horizons immediately after mentioning the probable existence of liquid oceans under Pluto's surface, a finding made possible thanks primarily to New Horizons.
It was a valuable piece of corroborating evidence, but not shocking and unexpected in the way results from those three missions were. We had good reason to believe Pluto would look a lot like Triton, and it does.
If there are planetologists reading the thread, I'd love to hear a more authorative perspective than mine!
> The radiation environment around Europa is punishing; an astronaut standing on the surface would get a fatal dose in about a day
Jupiter and Io have a very interesting symbiosis. Jupiter melts Io to form dusty volcanos. It then magnetically sweeps Io clean of dust. The dust forms a plasma ring that enhances the same magnetic field.
Io, meanwhile, is 35 Sv/day. Location really matters among the four Galilean moons.
> We want rocks in contact with water,
But there is ice compressed between the water column and the xenoceanic bottom, ok. I see the problem.
What about rocks in the surface of the water?. Some volcanic rocks can float.
This is... not something you lay plans on. Even on Earth, these rocks are formed at surface pressure, just barely float, and don't float for long (I've tried). If they form in the deep ocean, I'm guessing the pressure isn't going to let the bubbles be big enough to create bouyancy at all. Either way they would be super rare.